Needleless syringe devices are known from WO 94/24263. In this document, a needleless syringe is disclosed which entrains particles in a gas stream accelerated through a nozzle so that the particles may be injected into a target, such as human skin or other cells. For many applications, there is a need for the particles to be maintained in a sterile environment prior to actuation of the device. WO 94/24263 discloses for this purpose a particle cassette comprising a central annular ring having rupturable membranes bonded to each face so as to form a self contained sealed unit containing the particles to be injected. Upon actuation of the device, the membranes rupture allowing the particles initially contained between the membranes to be entrained in the gas flow and then delivered into the target. WO 94/24263 is hereby incorporated by reference.
An improvement to the particle cassette of WO 94/24263 is disclosed in WO 03/011379. In this document, a particle cassette comprised of two parts, each part having bonded thereto a rupturable membrane, is disclosed. In the preferred mode of manufacture, the membranes are heat-bonded to their respective cassette parts and the particle cassette is formed by bringing the cassette parts together so as to create a chamber for the particles. This overcomes the problem with the WO 94/24263 particle cassette that heat-bonding the second membrane to the annular ring can cause degradation of the particles in the chamber. WO 03/011379 is also hereby incorporated by reference.
FIG. 13 of WO 03/011379 shows a particle cassette having a first cassette part 70 with a membrane 71 heat-bonded thereto and a second cassette part 72 with a membrane 73 heat-bonded thereto. The first and second cassette parts are brought together in the longitudinal direction such that ribs on the external surface of the second cassette part interact with the inside annular surface 78 of a protrusion on a first cassette part. This provides an interference fit which holds the first and second cassette parts together. The particle cassette is designed to be assembled by hand.
A problem with such hand assembly is that the chamber 77 for the confinement of particles is not hermetically sealed. This has been confirmed by subjecting the particle cassette of FIG. 13 of WO 03/011379 to vacuum tests whereby it becomes evident that although the chamber 77 is sealed to the extent that the particles cannot escape, it is still possible for gases and even smaller particles (e.g. microbes) to infiltrate into the chamber 77. Accordingly, the present invention seeks to alleviate this problem.